BIOLOGIC CONSIDERATIONS FOR MAXILLARY IMPRESSIONS
BIOLOGIC CONSIDERATIONS FOR MANDIBULAR IMPRESSIONS
PRINCIPLES OF IMPRESSION MAKING
CLASSIFICATION OF IMPRESSIONS
IMPRESSION TECHNIQUES IN COMPROMISED SITUATIONS
• Complete denture impression procedures are
perhaps one phase on which much has been
spoken about. The literature on the subject shows
a persistent disagreement ever since 1850.
• Much of this confusion results from the fact that
many impression procedures have been
developed on empirical basis.
• Many have used the available knowledge of
functional and histological anatomy for the
development of their procedures, but the variation in
these techniques indicate a wide difference in
interpretation of the foundation of dentures.
• Whatever the method used it is generally agreed that
good impressions are basic for the construction of a
“Ideal impression must be in the mind of the dentist before it
is in his hand. He must literally make the impression rather
than take it”
- M.M. Devan
A negative likeness or copy in reverse of the surface
of an object .
– gpt 8
• An impression can also be defined as an imprint of
the teeth and adjacent structures for use in dentistry.
- gpt 4
• COMPLETE DENTURE IMPRESSION
A complete denture impression is a negative registration
of the entire denture bearing, stabilizing and border seal
areas present in the edentulous mouth
• PRELIMINARY IMPRESSION
A preliminary impression is an impression made for the
purpose of diagnosis or for the construction of a tray
A final impression is an impression for making the
master cast .
Any substance or combination of substances used for
making an impression or negative reproduction.
• Before the middle of the 18th century, no method
was available for producing an impression of the
alveolar ridge. A widely used method at that time
was the painting of the ridge with a dye , and the
pressing of a block of ivory or bone against the dyed
• Areas of contacts were scraped away from the block
until the best fit for the prosthesis was achieved
• 1756 – beeswax was apparently first used in making
impressions in the mouth.
Philip Pfaff(Berlin) made a sectional wax
impression of half of an arch at a time.
• 1782 -William Rae said that
“he got the measurement of the jaws in a piece of
wax pushed into the gum, afterwards making a cast
of it with plaster of paris”
• 1840 - Charles De loude (london) made one of the
earliest refrences to impression trays . He wrote
“for impressions, I use wax in tin cups or shapes, the
whole size of the upper and lower jaws, right or left, half
jaws and fronts.”
• 1842- Montgomery discovered gutta percha. It was
obtained from various sapotaceous trees in Malaysia. It
was introduced as an impression material in 1848 by
Colburn said it should be thoroughly soaked in boiling
water, kneaded and moulded in the same way as wax
and …. immediately place in the mouth, and firmly
pressed to the jaws.
• 1844- Plaster of paris
• Wescott, Dwinelle and Dunning have been credited
with this discovery.
• 1847 - Desirabode referred to an impression tray as
“ we place wax in a box, a kind of semi elliptical gutter
of tin or silver, upon the anterior part of which is a
shaft which forms a handle. The walls of this
receptacle offering some resistance, opposite the
deformation of the wax”.
Franklin described the first correct impression . He used
wax for the preliminary impression followed by a
Wescott described a similar technique using oversized
wax trays made by scooping out primary impressions
• 1874 - Use of impression compounds dates from
contributions of J.W.Greene, P.T.Greene and of
• The Greene brothers (about 1900) introduced a
modeling plastic , a method to manipulate it , and a
technique that is said to have been the first to utilize
all the surfaces of a mouth to advantage for denture
retention. They were probably the first to describe
the closed mouth all modeling plastic technique in
Furthermore, they were the first to use the word “ post
dam” in describing posterior palatal seal.
• 1915 - Rupert hall , perfected the first moderate heat
modeling plastic for making individual trays and
introduced the correctable modeling plastic-plaster
technique that became a standard method for
making an impression.
• Hall used a specially prepared hard black modeling
plastic for making a custom tray in which a very thin
mix of impression plaster was placed for correction.
• 1922- Everett described an early wax technique
around this time. He used fluid wax compound of
three consistencies: hard, medium and soft.
He said “ in every way possible represents the three
general tissues of the mouth on the bone”
• 1925- Alphous Poller (Vienna) described his elastic
material for “molding articles of all kinds, more
particularly, parts of a living body.
• He was most likely the first to suggest the use of agar
for dental impressions.
• Booth, however, described complete denture
impression technique using agar but found it
necessary to build custom water cooled trays and to
pre-medicate the patient with a drug to reduce
• During late 1920’s the idea became widely held that
uniform tissue support may be of value. It was
believed that this would be attained by controlled
placement of soft tissues.
• During this period, the first true functional
impression wax was developed. The waxes before
this (beeswax and parafinn wax) were far from ideal
because they were hard, flowed too slowly, or were
• 1930 - According to Applegate a series of true
physiologic waxes was developed by the cooperative
effort of G.C.Bowles , S.G.Applegate and himself and
was made availbale in 1935.
• Early 1930’s
First real impetus in use of zinc oxide eugenol for
impression materials came From A.W.Ward and
Ward’s preparation was intended more so for a surgical
pack , but he also said that it could also be used as
lining for dentures as an impression material .
Kelly’s preparation was primarily intended as an
Harry.L.Page introduced the mucostatic concept.
The advocates of this concept such as
Page, Albinson, Dykin and Addison thought the
universally accepted concept involving compression
of soft tissues and relief of the hard areas was in
error because hydrostatics proved that human
tissues was not amenable to either of this condition.
They believed that the impression should be an
absolute accurate negative of the ridge tissues at
Dirksen reported the findings of his research in IOWA
which resulted in the development of still another
physiologic impression wax. Over the years
functional waxes have grown steadily in popularity
and many clinicians have suggested methods for
– Applegate for immediate dentures
– Mc. Cracken, borkin, and faber for mandibular
– Hardy , ostrem and schultz for complete denture
Trapozzano described one of the early techniques
using Zinc oxide eugenol paste. Compound
preliminary impressions were made in stock trays
and plaster of paris casts were poured. Vulcanite or
shellac bases were constructed, on which occlusion
rims of wax or compound were placed. After a
tentative vertical and centric relation was established
, the final corrective impression was made using
closed mouth technique.
• 1942- Pendleton suggested a fluid wax technique
using asiatic or indian paraffin fro the final
• Wright and Denen suggested using alginate in a
border molded perforated customized acrylic tray.
• Collett described an alginate technique for the
maxillary impression using the material as a wash in
a modeling paste preliminary impression .
Elastomeric impression materials were introduced.
They were of two chemical types.
– Silicone base
• Pierson in 1955 reported on a new elastic material of
a polysulfide base (thiokol).
Shortly there after silicone base materials were
elastomeric impression materials were intended
primarily for making impressions for
• And for fixed partial dentures
• Chase in 1961 first described the moldable acrylic
material used for tissue conditioning and for
functional(dynamic) impression for complete
According to Emmett Beckley in 1973 , the first
moldable acrylic material consisting of an ethyl
methacrylate and an ethinol liquid was developed by
Clark Smith and he (Beckley) performed the first
practical research with this material in complete
• The bones of the upper and lower edentulous jaws
are covered with soft tissue, and the oral cavity is
lined with soft tissue known as mucous membrane.
• The denture bases rest on the mucous
membrane, which serves as a cushion between the
bases and the supporting bone.
• The mucous membrane is composed of two layers
The mucosa is formed by the stratified squamous
epithelium and a subjacent layer of connective
tissue known as the lamina propria.
• The submucosa is formed by connective tissue.
It may contain glandular , fat , or muscle cells and
transmits the blood and nerve supply to mucosa.
• The thickness and consistency of submucosa are
largely responsible for the support that the soft tissue
affords the denture, since in most instances the
submucosa makes up the bulk of the mucous
• In a healthy mouth the submucosa is firmly attached
to the periosteum of the underlying bone of the
residual ridge and will usually successfully withstand
the pressure of the denture.
HISTOLOGY OF THE MUCOUS MEMBRANE
COVERING CREST OF THE RESIDUAL RIDGE
• The oral mucosa is divided
in three catogories
depending on its location
in the mouth
• Masticatory mucosa
• Lining mucosa
• Specialized mucosa
The masticatory mucosa covers the
crest of the ridge
the residual attached gingiva firmly adherent to the
It is characterized by a well defined keratinized layer on
its outermost surface subject to changes in thickness.
The specialized mucosa covers the dorsal surface of the
tongue. This mucosal covering is keratinized.
The lining mucosa is generally devoid of the
keratinized layer. It is found to cover the :
mucous membrane of lips, cheek
ventral surface of the tongue and,
the unattached gingiva found on slopes of residual
FOR MAXILLARY IMPRESSIONS
If dentures and their supporting tissues are to coexist for reasonable length of time, the anatomy of
the supporting and limiting structures must be
understood for these are the foundations of the
denture bearing areas, as their role determines :
1. the selective placement of forces by denture bases
on supporting tissues
2. the form of the denture borders that will be
harmonious with normal function of limiting
structures around them.
The anatomical landmarks in the maxilla are:
• Limiting structures:
Posterior palatal seal area
• SUPPORT FOR THE
The ultimate support for
the maxillary denture is
the bone of the two
maxillae and the palatine
bone. The palatine
processes of the maxillae
are joined together at the
midline in the median
• RESIDUAL RIDGE:
The shape and size of the alveolar ridges change
when the natural teeth are removed. The alveoli
become mere holes in the jawbone and begin to fill
up with new bone, but at the same time the bone
around the margins of the tooth sockets begin to
shrink away. This shrinkage, or resorption, is rapid at
first, but it continues at a resorbed rate throughout
The maxillary labial frenum
is a fold of mucous
membrane at the median
No muscle attachment.
This band of tissue starts
superiorly in a fan shape
and converges as it
descends to its terminal
attachment on the labial
side of ridge.
This anterior region of maxillary basal seat extends
from one buccal frenum to the other on the labial side.
The major muscle in this area is orbicularis oris.
Three objectives are apparent:
The impression must supply sufficient support to the
upper lip to restore the relaxed contour.
The labial flange of the impression must have sufficient
height to reach the reflecting mucous membrane of the
labial vestibular space.
There must be no interference of the labial flange with
the action of lip in function.
• Buccal Frenum:
The buccal frenum is sometimes a single fold of
mucous membrane, sometimes double, and in some
mouths, broad and fan shaped.
Associated muscles are:
Levator anguli oris
• Buccal Vestibule:
The buccal vestibule extends from the buccal frenum
to the hamular notch.
It is influenced by the buccinator and the modiolus.
And distally by the coronoid process.
• Hamular Notch:
The hamular notch is a displaceable area about 2mm
wide , between the tuberosity of the maxilla and the
hamulus of the pterygoid plate.
• Vibrating Line Of The Palate:
This is an area at or distal to the junction of hard and
soft palate where movement occurs when patient
This generally is not a line and should be described
rather as an area.
The area may also be identified by “Valsalva
maneuver ” by asking the patient to close his nose
using his fingers and asking him to blow gently
through the nose .
• Posterior vibrating line
that is 4-12mm or on an
average is 8.2 mm
dorsally to the hard and
soft palate junction. In
most instances the
denture should end 1 or
2mm posterior to the
vibratory line .
• Maxillary Tuberosity:
tuberosities are the
distal aspects of the
The considerations for the mandibular impressions
are generally similar to that for those of maxillary
impressions and yet there are many differences
owing to the following facts:
– The basal seat of mandible is different in size and
form from the maxillary counterpart.
– The submucosa in some parts of mandibular basal
seat contains anatomic structures different from
those in the upper jaw.
– The nature of the supporting bone on the crest of
residual ridge usually differs between the two
– The presence of the tongue complicates the
impression procedures for the lower denture.
– The available area of support from an edentulous
mandible is 14 cm2 while the same for the
edentulous maxilla is 24cm2 .
– The supporting and the peripheral sealing areas
will be in contact with the dentures fitting or
impression areas. The support for the mandibular
denture is derived from the body of mandible.
Crest of the residual alveolar ridge
Buccal shelf area
• The area between the
mandibular buccal frenum and
the anterior edge of the
masseter is known as the
• It is bounded medially by the
crest of the residual ridge
, anteriorly by the buccal
frenum , laterally by the
external oblique line and
distally by retromolar pad.
• The buccal shelf forms the primary support for the
mandibular denture as it is made primarily of cortical
type of bone.
• The buccal shelf area can range from 4-6 mm wide
on an average mandible to 2-3 mm or less in narrow
• The buccal shelf is very wide and is at right angles to
the vertical forces of occlusion. For this reason it
offers excellent resistance to such forces.
Crest Of The Mandibular Ridge
• The crest is covered by the fibrous connective
tissue, but in many mouths the underlying bone is of
cancellous type without a cortical bony plate
• The fibrous connective tissue is favorable for
resisting the externally applied forces,such as the
denture. However, with the underlying cancellous
bone this advantage is lost .
• This is single narrow band but may consist of 2 or
• The activity of this area tends to be vertical so the
labial notch on the denture should be narrow.
• This is usually in the area of 1st pre molar. The oral
activities in these area are horizontal as well as
vertical (ex. Grinning and puckering) thus needing
• The contour of the denture will be little narrower in
this area due to the activity of depressor anguli oris
• It is the sulcus between the buccal frenums.
• The major muscle in this area is orbicularis oris
whose fibers are mainly horizontal thus
overextension in this area should be avoided.
• The buccal vestibule extends from the buccal frenum
posteriorly to the outside back corner of the
retromolar pad and from the crest of the residual
alveolar ridge to the cheek.
Pear Shaped Pad:
• The retromolar pad as
described by Sicher is
described as the soft
elevation of mucosa that
lies distal to the third molar.
• It contains loose connective
tissue with an aggregation
of mucous glands and is
bounded posteriorly by the
temporalis tendon , laterally
by the buccinator, and
medially by the
and the superior constrictor.
• It can be divided into three areas
anterior vestibule/sublingual crescent area/ anterior
the middle vestibule/ mylohyoid area
the distolingual vestibule/ lateral throat form/
Anterior lingual vestibule
• This extends from the lingual frenum to where the
mylohyoid ridge curves down below the level of
sulcus. Here a depression the premylohyoid fossa can
• This is mainly influenced by the genioglossus
muscle, lingual frenum and some part by anterior
portion of sublingual glands .
• This is the largest area and is mainly influenced by
mylohyoid muscles and somewhat by sublingual
• The mylohyoid muscle is the largest muscle in the
floor of the mouth whose principal function occurs
during swallowing. Its intra oral appearance is
misleading because the membranous attachment
makes the muscle appear to be horizontal when
• Nagel and sears have shown that at maximum
contraction the fibers are still in a downward and
forward direction so that a denture can be extended
below the muscle attachment along the mylohyioid
• The lingual borders in the mylohyoid areas are
formed by contact with the mylohyoid muscle in
functional, but not extreme, contracted or elevated
• The average mylohyoid border is 4-6 mm beyond the
mylohyoid ridge in fair to good ridge it is about 2-3
mm . If the ridge is flat it is often advantageous to
make mylohyoid border thicker (4-5mm or more).
• The lateral throat form is bounded anteriorly by
mylohyoid muscle, laterally by pear shaped
pad, posterolaterally by superior
constrictor, posteromedially by palatoglossus and
medially by tongue.
• The so called “s” curve of the lingual flange of the
mandibular denture results from stronger intrinsic
and extrinsic tongue muscles, which usually place
the retromylohyoid borders more laterally and
towards the retromylohyoid fossa, as the oppose
weaker superior constrictor muscle.
• The posterior limit of the mandibular denture is
determined mainly by the palatoglossus muscle and
somewhat by weaker superior constrictor muscle
this is area is called posterior/ retromylohyoid
• Neil described this area and noted that the denture
could have three possible lengths, depending on the
tonicity, activity, and anatomic attachments of the
adjacent structuresClass III lateral throat form has minimum length and
thickness. The border usually ends 2-3 mm below
the mylohyoid ridge or sometimes just at the ridge.
Class I throat form: The horizontal border is usually
2-3 mm thick, but a thicker border of 4-5 mm should
be used for better seal if the ridge is flat. The
retromylohyoid curtain area should be thinner, about
2-3 mm, and very rounded and smooth.
Class II throat form is about half as long and narrow
as class I and about twice as long as class III.
BASIC REQUIREMENTS FOR
• Knowledge of Basic anatomy
• Knowledge of basic reliable technique
• Knowledge and understanding of impression
• Patient management
OBJECTIVES OF IMPRESSION
PRESERVATION OF REMAINING
Retention is defined as that state of a denture
wherein functional forces are unable to destroy the
attachment existing between the denture and the
Retention resists the adhesiveness of food, the force
of gravity, & the forces associated with the opening
Retention begins with the impression. It depends
upon factors that produce attachment of the denture
to the mucosa.
Factors affecting Retention
Size of the denture bearing area
Quality of the denture bearing area.
Factors affecting Retention
Saliva and its quality
Factors affecting Retention
Interfacial surface tension
Capallarity and capillary attraction
Atmospheric pressure and peripheral seal
Adhesion :It is the physical attraction of unlike molecules
• It acts when saliva sticks to the denture base & to
the mucous membrane of basal seat .
• Adhesion is achievied by ionic forces between
charged salivary glycoproteins & surface epithelium
or acrylic resin.
• Quality of adhesion depends on :-
• The most adhesive saliva is thin serous but contains
some mucous components.
• Thick & ropy saliva is very adhesive but tends to build
up so that it is too thick in palatal area & interferes
with oral adaptation .
• In this situation patient should rinse out the ropy
saliva every two to three hours
• The amount of retention provided by adhesion is
directly proportional to the area covered by denture.
• Mandibular dentures cover less surface area than
maxillary prosthesis & therefore are subject to a
lower magnitude of adhesive retentive forces.
• Similarly patients with small jaws or very flat alveolar
ridges cannot expect retention to be as great as can
patients with large jaws or prominent alveoli.
Cohesion:-it is the physical attraction of like molecules
for each other .
• it occurs within the layer of fluid (usually saliva ) that
is present between the denture base & the mucosa.
• Normal saliva is not very cohesive , therefore most of
the retentive forces of denture –mucosa interface
comes from adhesive & interfacial surface tension
Interfacial surface tension :-it is the resistance to
separation of two parallel surfaces that is imparted
by a film of liquid between them .
It is dependent on the ability of the fluid to wet
the rigid surrounding material .
If the surrounding material has low surface tension
, as oral mucosa does ,fluid will maximize its contact
with the material, thereby wetting it readily &
spreading out in a thin film.
If the material has high surface tension ,fluid will
minimize its contact with the material , resulting in
formation of beads on the material surface.
• All denture base material have higher surface tension
than oral mucosa ,but once coated by salivary pellicle
,their surface tension is reduced ,which promotes
maximizing the surface area between liquid & base.
• Role of surface tension is through capillary attraction
• When the adaptation of denture base to mucosa is
sufficiently close ,the space filled with a thin film of
saliva act like a capillary tube in that the liquid seeks
to increase its contact with both denture & mucosal
• It plays a major role in retention of maxillary denture.
It is totally dependent on presence of air at the
margin of liquid & solid contact (liquid air interface).
• As there is excess saliva along the lower border of
mandibular denture, Surface tension is lost in
mandibular denture due to loss of liquid air interface
at denture border .
Mucostatics dismiss adhesion and cohesion as
factors in retention, the entire phenomenon being
attributed to interfacial surface tension.
But an analysis has proved that if it was not for the
forces of adhesion and cohesion, the forces of
interfacial surface tension wont exist. Attachment of a
denture is possible because both tissue and denture
base material can become wet which means its
molecule will adhere to water molecules.
Oral & facial musculature :-supplement retentive forces
, provided :a)Teeth are positioned in “neutral zone “between the
cheeks & tongue
b)The polished surface of the denture are properly
• If the buccal flange of maxillary denture slope up &
out of occlusal surface of teeth & the buccal flange of
mandibular denture slope down & out from the
occlusal plane, the contraction of buccinator will
tend to retain both denture on basal seat.
Atmospheric pressure:• Act to resist dislodging forces applied to the denture
,if the denture have an effective seal around their
• Retention due to atmospheric pressure is directly
proportional to the area covered by the denture
In function, atmospheric pressure is superior to
interfacial surface tension as a retentive force, for
forces horizontal as well as parallel to the mean of
mucosal plane are resisted.
Interfacial surface tension will resist only forces
perpendicular to the axis of surface tension forces.
Factors affecting Retention
The muscles apply supplementary retentive
forces on the denture.
It is most effective in the neutral zone.
The quality of a denture to be firm, steady, or
constant, to resist displacement by functional
stresses and not to be subject to change of position
when force is applied. It is the ability of the denture
to withstand horizontal forces.
Factors Affecting Stability
Vertical height of the residual ridge.
Quality of soft tissue covering the ridge.
Quality of the impression.
Contour of the polished surfaces.
• It is the resistance to vertical forces of mastication &
to occlusal or other forces applied in a direction
toward the basal seat .
• When the natural teeth are missing ,the alveolar
ridge & their covering of mucosal tissue become the
• Unfortunately , they were never meant to endure the
forces of mastication & other constant occlusal
pressure that result from swallowing , clenching ,or
• To make the best of bad situation , it is necessary to
enhance the available support by utilizing maximum
coverage of all usable ridge bearing areas.
Areas of support are divided into:-
Primary support area:- area of edentulous ridge that
are at right angle to occlusal forces & usually do not
resorb easily .
• Maxillary:a)posterior ridge
b) flat areas of the palate
• Mandibular:a)buccal shelf area
c)pear shaped pad
Secondary supporting area:- area of edentulous ridge
that are greater than at right angle to occlusal forces
; also the area of dentulous ridge that are at right
angle to occlusal forces but tend to resorb under
• Maxillary :- anterior ridge ,rugae & all ridge slopes
• Mandibular:- anterior ridge & all ridge slopes
The thickness of the denture flanges is one of the
important factors that govern esthetics.
Thicker denture flanges are preferred in long-term
edentulous patients to give required labial fullness.
Impression should perfectly reproduce the width and
height of the entire sulcus for the proper fabrication of
PRESERVATION OF REMAINING STRUCTURES
De Van (1952) stated that, “the preservation of that
which remains is of utmost importance and not the
meticulous replacement of that which has been lost.
Impressions should record the details of the basal
seat and peripheral structures in an appropriate form
to prevent injury to the oral tissues.
on the tray
Depending on theories of impression making
Mucostatic or Passive Impression
First proposed by Richardson and later popularised by
The impression is made with the oral mucous
membrane and the jaws in a normal, relaxed condition.
Border moulding is not done here.
The impression is made with an oversized tray.
Impression material of choice is impression plaster.
Retention is mainly due to interfacial surface tension.
The mucostatic technique results in a denture, which
is closely adapted to the mucosa of the denturebearing area but has poor peripheral seal.
Records the oral tissues in a functional and displaced form.
The materials used for this technique include impression
compound, waxes and soft liners.
The oral soft tissues are resilient and thus tend to return to
their anatomical position once the forces are relieved.
Dentures made by this technique tend to get displaced due to
the tissue rebound at rest. During function, the constant
pressure exerted onto the soft tissues limit the blood
circulation leading to residual ridge resorption.
Selective Pressure Impression (Boucher)
In this technique, the impression is made to extend over as
much denture-bearing area as possible without interfering
with the limiting structures at function and rest.
The selective pressure technique makes it possible to confine
the forces acting on the denture to the stress-bearing areas.
This is achieved through the design of the special tray in
which the non stress-bearing areas are relieved and the
stress-bearing areas are allowed to come in contact with the
Depending on the technique
Open mouth impressions
The open mouth impression is built in a tray which carries
the impression material of choice into the desired
contact with the supporting tissues and into an
approximate relation to the peripheral tissues when the
mouth is opened and without applied pressure.
The rationale behind this method is that the dentures do
not dislodge when subjected to biting force.
The open mouth methods provide clearance for the
tissues that are pulled over the edges of the
dentures as in function of speech.
It develops a contour of impression surface which is
in harmony with the relaxed supporting tissues, and
which may be out of perfect adaptation with these
tissues when the denture is subjected to occlusal
Closed mouth impression technique
These require wax occlusal rims to be fabricated on
the preliminary cast .
The patient is made to close on these rims and a
generous clearance is made for the various frenula so
that the patient can manipulate his tissues by
closing, grimacing, sucking and swallowing to form
Depending on the tray type
Type of tray
Some dentists use a stock tray and an impression
material such as alginate , impression plaster or
impression compound is used .However such
impressions are generally overextended and serve as
On casts made from these primary
impressions, special/custom trays are fabricated. The
tray is tried in the mouth and modified and the final
impressions are made using zinc oxide eugenol or
other such materials.
Depending on the purpose of the
The negative replica of the oral tissues used to prepare a
for study purposes like measuring
undercuts, locating the path of insertion.
Is made as a part of treatment plan and to estimate the
amount of pre-prosthetic surgery.
Articulate the casts on tentative jaw relation and evaluate
the inter-arch space.
An impression made for the purpose of diagnosis or for the
construction of a tray.
There should be at least 5mm clearance between the
stock tray and the ridge.
The tray should extend over hamular notch and maxillary
tuberosity. Mandibular tray should cover retromolar pad.
Tray can be extended using modelling wax.
Impression compound, Alginate, Impression plaster
Fabriction of custom tray.
Developing the posterior palatal seal.
Making the wash impression.
Depending on the material used
Impression techniques may be classified
a) Amount of pressure used
1. Pressure technique
2. Minimal pressure technique
3. Selective pressure technique
b) Based on the position of the mouth while making
1. Open mouth
2. Close mouth
c) Based on the method of manipulation for border
1. Hand manipulation
2. Functional movements
Pressure theory or mucocompressive
• This theory was proposed on the assumption that
tissues recorded under functional pressure provided
better support and retention for the denture.
• Greene in 1896 gave this concept
Primary impression made with impression
Special tray made using shellac base plate.
Second Impression is made in this tray using
Bite rims with uniform occlusal surfaces are then
Areas to be relieved are softened and the
impression is inserted in mouth and held under
biting pressure for one or two minutes.
Borders are molded by asking the patient to
perform functional movements.
Demerits of the theory
1. Excess pressure could lead to increase alveolar
2. Excess pressure was often applied to the peripheral
tissues and the palate.
3. Dentures which fit well during mastication tend to
rebound when the tissue resume their normal
4. Pressure on sharp bony ridges results in pain.
• The technique tells that border tissues are recorded
in their functional positions and denture cannot be
dislodged during functional movements of jaws.
• The pressure applied is more and directed towards
the palate and peripheral tissues. So the retention
will be for short time and will be lost as soon as the
bone undergoes resorption.
• Usually this technique is used for preliminary
impression making as it gives a positive peripheral
seal and tissues are recorded in function. Amount of
pressure applied is for short duration and the areas
can be relieved during the final impression.
Minimal pressure or mucostatic theory –
The main advantage of this technique is its high regard
for tissue health & preservation.
• 1946 Page gave the concept of mucostatic based on
• A compound impression is made.
• A baseplate wax space is adapted.
• A special tray is adapted over the wax spacer.
• Spacer is removed and an impression is made with a
free flowing material with little pressure.
• Escape holes are made for relief.
• The short denture borders are readily accessible to the
tongue which might provoke irritation.
• The lack of border molding reduces effective peripheral
• The short flanges may reduce support for the face.
• The shorter flanges prevent the wider distribution of
• The shorter flange would mean less lateral stability.
• The technique holds good in the sense it helps in
preservation of tissue health.
• In practice with short flanges the oral musculature is non
supported and stresses are not widely distributed.
• Food can slip beneath the denture and tongue can
readily access the denture borders.
• This technique is useful in impressions of flabby and
sharp or thin ridges.
Selective pressure theory
• Advocated by Boucher in 1950 it combines the
principles of both pressure and minimal pressure
• In this technique idea of tissue preservation is
combined with mechanical factor of achieving
retention, through minimum pressure which is
within physiologic limits of tissue tolerance.
• This theory is based on a thorough understanding
of the anatomy and physiology of basal seat and
• Some feel that It is impossible to record areas with
• Some areas still recorded under functional load, the
dentures still faces the potential danger of
rebounding and loosing retention.
• Inspite of some of its apparent drawbacks all the
impression techniques based on the selective
pressure technique are still popular.
• Final impressions using this technique are made
where relief areas are provided and pressure is
distributed on the stress bearing areas.
Open mouth technique
Made with tray held by dentist and mouth open
Muscle movements may be emphasized and
can be seen by the operator
Closed mouth technique
The rationale behind this technique is that the
supporting tissues are recorded in a functional
Requires occlusal rims to be made
Border molding done and final impressions made
Dentist uses hand manipulation for movements of
lips and cheeks
Patient makes functional movements such as
sucking, swallowing, licking or grinning
STEPS IN MAKING AN IMPRESSION
Preliminary examination of the patient
Seating the patient
Selection of the tray
Selection of the material
Preliminary examination of the patient
• A complete case history and thorough clinical
examination is done.
• Factors that can complicate impression making are
• Patient education.
Seating of the patient
Position of the operator for
Position of the operator for
Selection of tray:
• The beginning of good impression starts with the
selection of the correct stock tray.
• Tray is a device that is used to carry, confine and
control impression material while making an
• The space available in the mouth for upper
impression is studied carefully by observation of the
width and height of the vestibular spaces with mouth
• And in the lower the general form and size of basal
seat is studied.
• First technique:- border- molded special tray:
An edentulous stock metal tray that is approximately 6mm larger
than the outside surface of the residual ridge is selected.
The borders of the stock tray are lined with a strip of soft boxing
wax so a rim is created to help confine the alginate material.
The objective is to obtain a preliminary impression that is slightly
overextended around the borders.
The tissue surface and borders of the tray, including
the rim of wax, are painted with an adhesive
The loaded tray is positioned in the mouth.
The tray is left in the mouth for 1 minute after the
initial set. The impression is removed and inspected
to ensure all basal seat is included.
The impression is poured in artificial stone.
Primary impression making
• With alginate (Maxillary)
A wax spacer is placed within the outlined border to
provide space in the tray for final impression
A custom tray made using self- curing acrylic resin.
• Preparing the final impression tray:
Border molding is the process by which the shape of
the borders of the tray is made to conform accurately
to the contours of the buccal and labial vestibules.
It begins with manipulation of the border tissues
against a moldable impression material that is
properly supported and controlled by tray.
Stick modeling compound is added in sections to the
shortened borders of the resin tray and molded to a
form that will be in harmony with the physiologic
action of the limiting anatomic structures.
The final impression material is mixed according to
manufacturer’s directions and uniformly distributed
within the tray.
• Second technique:- one- step border- molded tray:
• A material that will allow simultaneous molding of all
borders has two general advantages:
1. The number of insertions of the tray for maxillary
and mandibular border molding is reduced.
2. Developing all borders simultaneously avoids
propagation of errors caused by a mistake in one
section affecting the border contours in another.
• The requirements of such a material are that it
1. Have sufficient body to allow it to remain in
position on the borders during loading of the tray.
2. Allow some preshaping of the form of the borders
without adhering to the fingers.
3. Have a setting time of 3 to 5 min
4. Retain adequate flow while the tray is seated in the
5. Allow finger placement of the material into
deficient parts after the tray is seated
• Not cause excessive displacement of the tissues of
• Be readily trimmed & shaped so excess material can
be carved & the borders shaped before the final
impression is made.
• The following procedure utilizes polyether
impression materials for border molding.
1. Place adhesive for polyether impressions on the
borders of tray.
2. Express a 3- inch strip of polyether material from
large tube onto a mixing pad. Next express 2.5
inches of catalyst to provide sufficient working time
to complete border molding.
3. Thoroughly mix material for 30 to 45 seconds using
a metal spatula.
4. Position the polyether material on the borders, making
certain that a minimum width of 6 mm exists on inner
5. Quickly preshape material to proper contours with
fingers moistened in cold water
6. Place the impression tray in the mouth .
7. Inspect all borders to be sure that impression material is
present in the vestibule
8. Border molding is done
9. Remove tray when impression material is set.
10. Examine border molding to determine that it is
• Preparing the tray to secure the final
1. Reduce the borders on the tray that protrude
through the polyether.
2. Remove any material that extends internally within
the tray more than 6mm.
3. Remove the relief wax.
4. Reduce the thickness of labial flange to
approximately 2.5 to 3mm from one buccal frenum
5. Make the final impression in silicone, metallic oxide
paste, or rubber base.
• Third technique:- custom tray design based on
previously worn denture:
1. The denture is treated like a standard
impression, and a stone cast is poured.
2. An acrylic resin tray is made on the cast over a wax
spacer that is outlined just short of the borders of
3. The tray is tried in the mouth and checked for
4. The spacer is removed, relief holes prepared, an
adhesive is applied and an impression is made in
the preferred material.
SPECIAL IMPRESSION TECHNIQUES
IMPRESSIONS OF UNSUPPORTED MOVABLE TISSUES
IMPRESSION PROCEDURE FOR THE SEVERELY
WAX BASE DEVELOPMENT FOR COMPLETE DENTURE
• Jaggers, Shay and Khan : Impressions of
unsupported movable tissues; JADA october 1981, 103;
• In conditions where
patients have worn
denture opposed only
by mandibular anterior
• KELLY (1972)
introduced the term
• The remaining soft tissues in the anterior maxillary
region are easily distorted by routine impression
procedures, resulting in an unstable denture base.
• Surgical reduction of the pliable tissues often results
in the loss of the anterior mucobuccal fold area.
this may cause retention problems
• To avoid these
problems, a technique
edentulous arches with
tissues are made is
• A primary impression is made and
a cast is poured.
• An indelible pencil is used to
outline the unsupported movable
• A single custom tray is made, and
an opening is cut in the tray as
indicated by the transfer of
indelible pencil line.
• Modelling plastic is adapted bilaterally on the
posterior aspect of the tray to act as handles.
• The tray is adjusted in the mouth, and a routine
border molding is formed.
• The tray is painted with
an adhesive and a
regular body impression
• The excess material is
trimmed to the outline
of the aperture
• The completed base impression is returned to the
• This impression does not touch the unsupported
• Then a highly mucostatic
material, impression plaster
is brushed on the
• The initial layer precludes
entrapment of air and
enables visualisation of the
• A separating media is
applied to the
impression plaster and
the master cast is made
AN IMPRESSION PROCEDURE FOR THE SEVERELY
ATROPHIED MANDIBLE : JPD 1995 ; 73(6); 574-577
• The objective is to maximize the supportive aspect of
the available denture foundation by two approaches
• Peripheral borders are developed functionally with
the mouth closed
• The final phase of impression is made with the
mouth open to satisfy the anatomic approach
• A maxillary final impression is made and cast is
• Construct a record base for the maxillary cast and
develop a flat wax occlusal rim.
• Make a preliminary impression of the mandible and
make a lower tray to be used initially as a record
base with a flat wax occlusion rim.
• Make a jaw registration at a selected vertical
dimension of occlusion.
• Develop the border
extensions with tissue
• Develop the lingual borders
with the mouth open and
have the patient make
• Also instruct the patient to
border mold the material
physiologically by producing
“ooo” and “eee” sounds
while biting on the occlusal
• Repeat the step as often as necessary to develop
• Relieve the tray wherever it shows through the
conditioning material before each subsequent
• Remove overextensions with a hot knife blade.
• Leave each application of
conditioning material in the
mouth approx. 10 minutes
to allow it to stabilize.
• After the desired extensions
are formed with the
conditioning material, make
the final second impression
with a polysulfide rubber
impression material with
the mouth open and use
standard border molding
• Pour the cast
immediately to avoid
distortion of the
• This procedure will provide the patient with a
denture that has function with maximum support
• The greatest disadvantage of this procedure is the
amount of the time necessary to develop the final
impression. The average appointment time needed is
• Appelbaum and Rivetti : WAX BASE
DEVELOPMENT FOR COMPLETE DENTURE
IMPRESSIONS; JPD; may 1985; 53(5); 663-666
• The objective of the denture base development is
the retention and stability.
• The retention enhancing potential of the border seal
and the effect of properly contoured and polished
surfaces against a functioning musculature must be
• Denture base retention is maintained by a constantly
changing interplay between the physical and
physiologic forces during speech, mastication, and
• The physiologic forces are mainly muscular and are
exerted by the lips, cheeks, and tongue.
• And the physical forces include
cohesion, adhesion, and interfacial surface
tension, which operate in the film of saliva between
the denture and the tissues.
• Three objectives of base development to secure
optimum retention and stability must be attained :
1) The impression procedure and material of choice
should permit the detailed reproduction of healthy
mucosa and ridge bearing tissue at rest to secure
optimum retention by interfacial surface tension
acting on the base through the medium of saliva.
2) The base should be extended to, but not
encroach on, functional muscle attachments to
permit greater distribution of masticatory stresses
and a greater surface for the development of
interfacial surface tension, which leads to the
production of the border seal.
3) The base should be adapted to the musculature of
the oral cavity to secure active and passive muscular
fixation of denture base, because the importance of
muscle activity may transcend all other factors
responsible for denture retention.
The most important muscle in this regard are the
buccinator, orbicularis oris, and intrinsic and extrinsic
muscles of the tongue.
Developing the base with mouth
• A preliminary functional impression tray with wax
occlusion rims is made with an opposing occlusion
rim or denture.
• The tray trimmed to relieve functioning muscle
• A closed mouth impression with mouth temperature
wax is made to establish maximum coverage within
• The IOWA wax is prepared in a container in a hot
water bath and is applied to the tray with a soft
brush. (firm contact produces glossy surface)
• After full ridge tissue contact is made, wax is applied
to the borders and is adapted to the functioning
musculature to develop the border and flanges of
• Essential actions :
- Protrusion and retrusion of the lips for the facial musculature
- Moving the mandible laterally and protrusively to record
coronoid process of mandible
- Placing the tongue alternatively into the cheeks and by
wiping the lips by the tongue to develop lingual and
retromylohyoid flange of mandibular tray
• The impression is allowed to remain in the mouth
and allowed to remain for 8 to 12 minutes to permit
as close adaptation of the wax to all surfaces as
• During this period, the patient periodically performs
the approppriate muscle functions. And then ice-cold
water is poured into the mouth to chill the wax, and
the impression is carefully removed.
• Impression is boxed by plaster
and pumice and cast is poured.
• Separating media is applied on
the cast and after the separating
media has dried, an
autopolymerising soft resilient
liner is applied to the undercuts.
• Spacer is applied and a resin tray
• When the tray resin has set, the
bottom side of the cast is reduced
on a cast trimmer just short of
contact with the tray material.
• The cast with tray is placed in hot
water to soften the wax shim and
the cast is fractured with a
hammer to permit recovery of
the tray without damage
• Wax spacer is removed, and
excess resin is removed from the
• The final impression
material, metallic oxide paste is
mixed according to
manufacturer’s directions and
loaded into the tray.
• Impression material is wiped
along all the flanges of the
impression tray in contact with
• The patient is instructed to perform the previously
described muscular movements while the impression
material is developing its body.
• The tray is removed from the mouth after the
material has set and the impression is inspected.
• This technique permits the harnessing and stabilizing
effects of an active musculature to operate on the
ultimate denture base.
• The musculature imparts properties of retention and
stability to the base that will tend to provide the
greatest longevity for the residual alveolar ridge.
• Most of the difficulties encountered when making
impressions can be traced to the operator’s lack of
attention to details of technique, and especially the
acceptance of a poor stock tray impression.
• It is of extreme importance that the preliminary
impression records the entire possible denturebearing surface but, at the same time, does not
encroach on movable muscular tissues.
• Impressions for complete dentures- Bernard Levin
• Boucher’s prosthodontic treatment for edentulous
patients- 10th edition.
• Appelbaum and Rivetti : Wax base development for
complete denture impressions; JPD; may 1985; 53(5);
• Richard P Frank: Controlling pressures during complete
denture impressions.; Dental Clinics of North AmericaVol 14, No.3 (July, 1970)
• Evaluation of factors necessary to develop stability in
mandibular dentures: J Pros. Dent May- June, 1966.
• DeFranco and Sallustio : An impression procedure for
the severely atrophied mandible; JPD; june 1995;
• Jaggers, Shay and Khan : Impressions of unsupported
movable tissues; JADA october 1981, 103; 590-592